Reflexes, or reflex actions, are involuntary, almost instantaneous movements in response to a specific stimulus. Reflex arcs that contain only two neurons, a sensory and a motor neuron, are considered monosynaptic. Examples of monosynaptic reflex arcs in humans include the patellar reflex and the Achilles reflex.
A microwave oven uses microwaves. This is a kind of electromagnetic wave. The energy source for the microwave oven is AC (alternating current, electricity), available in many houses.
Microwaves are a type of electromagnetic wave (shocker, right?), just like UV rays and radio waves. Instead of cooking food with heat like a conventional oven, microwave ovens excite atoms (or get 'em all moving around), cooking food evenly throughout rather than from the outside in (like an oven does).